A known valve timing control apparatus is installed in a drive force transmission system, which transmits a drive force from a crankshaft (serving as a drive shaft) of an internal combustion engine to a camshaft (serving as a driven shaft) that opens and closes intake valves or exhaust valves.
The valve timing control apparatus includes a housing and a vane rotor. The housing is rotated when the drive force of the crankshaft is transmitted to the housing. The vane rotor is rotatable relative to the housing and is fixed to the camshaft. The vane rotor partitions each of oil pressure chambers formed in an inside of the housing into an advancing chamber and a retarding chamber. When the oil, which is pumped by an oil pump, is supplied to one of the advancing chamber and the retarding chamber in each corresponding oil pressure chamber through one of two oil passages (one of two oil passage systems) formed in the engine side, the oil, which is accumulated in the other one of the advancing chamber and the retarding chamber, is returned to an oil pan through the other one of the oil passages. In this way, in the valve timing control apparatus, the vane rotor is rotated relative to the housing to change the relative rotational phase between the crankshaft and the camshaft to adjust the opening timing and the closing timing of the intake valves or the exhaust valves.
In the valve timing control apparatus, due to a resilient force of a spring, which urges the intake valve or the exhaust valve driven by the camshaft in a valve closing direction, a cam torque, which swings the vane rotor fixed to the camshaft in a retarding direction or an advancing direction, is exerted.
In view of the above point, a valve timing control apparatus recited in JP3033582B2 has a lock pin that limits relative rotation between the housing and the vane rotor. When the oil pressure is low at the time of starting the engine, the lock pin is received in a receiving hole of a vane rotor and is inserted into a fitting hole formed in the housing. In this way, the lock pin can limit collision between the housing and the vane rotor caused by the cam torque transmitted from the camshaft, and thereby generation of noise (hitting sound) can be limited.
After the starting of the engine, when the oil pressure is supplied to a pressure chamber formed in the fitting hole of the lock pin, the lock pin is removed from the fitting hole. Thereby, in the valve timing control apparatus, the relative rotation between the housing and the vane rotor is enabled.
The inventors of the present application have found occurrence of the following disadvantage in a state where the engine side oil passage is nearly clogged upon increasing of the viscosity of the oil under an extremely low temperature, or a state where the engine side oil passage is clogged by, for example, a foreign object.
That is, at the time of engine stop, the two oil passages (two oil passage systems), which connect between the oil pump of the engine and the valve timing control apparatus, as well as the retarding chambers and the advancing chambers of the valve timing control apparatus are filled with the air. In a case where the valve timing control apparatus adjusts the valve timing (the opening timing and closing timing) of the intake valves, the oil is supplied from the oil pump to the retarding chambers through one of the oil passages at the time of engine start. At this time, the air, which is accumulated in the one of the oil passages, is conducted to the advancing chambers and the pressure chamber of the lock pin after passing through a gap between the housing and the vane rotor. At this time, when the other one of the oil passages, which discharges the oil from the advancing chambers in the normal time, is clogged or nearly clogged, the air in the advancing chambers and the air in the pressure chamber are not discharged. Thus, a gas pressure of the pressure chamber is increased to possibly cause release of the lock pin. In such a case, the housing and the vane rotor cannot be fixed to each other. Thus, collision repeatedly occurs between the vane rotor and the housing to generate the noise (hitting sound).
In another case where the valve timing control apparatus adjusts the valve timing of the exhaust valves instead of the intake valves, the relationship between the retarding chambers and the advancing chambers discussed above may be reversed to understand the mechanism of generating the noise.